1. Field of the Invention
The present invention relates to an optical pickup device having a light emitting element provided in a holder which is superior in heat dissipation and is resistant to damage.
2. Description of Related Art
FIG. 7 shows an embodiment of a conventional optical pickup device.
Laser diodes (abbreviated as “LDs”) emit a laser beam and are also referred to as light emitting elements. LD drivers will be hereinafter abbreviated as “LDDs”. Referring to FIG. 7, an LDD 510 is a laser drive circuit for driving an LD 520 to cause the LD 520 to emit a laser beam. Electric current from the LDD 510 is supplied to the LD 520, which then emits a laser beam for recording information on a disk 700 and/or reading information recorded on the disk 700.
The laser beam which is emitted from the LD 520 is irradiated, through a diffraction grating 530, an intermediate lens 540, a half mirror 550, and an objective lens 560, onto the disk 700. A part of the laser beam reflected by the disk 700 impinges on a photo diode IC (which will be abbreviated as PDIC) 570. The PDIC 570 converts a light signal indicative of the received light beam into an electric signal, which is used to operate a servo mechanism (not shown) of a lens holder (not shown) of an optical pickup device 501. PDICs, which detect light irradiated thereto, are also referred to as photo detectors. The servo as described herein refers to a mechanism which measures a state of a control object and compares the measurement result with a predetermined reference value for automatically performing correction control.
Further, a part of the laser beam output from the LD 520 enters a front monitor diode (FMD) 580. The FMD monitors laser beams emitted by the laser diode for providing feedback to control the laser diode.
The LDD 510, the LD 520, the diffraction grating 530, the intermediate lens 540, the half mirror 550, the objective lens 560, the PDIC 570, and FMD 580 are mounted in a housing which is not shown. Further, the LDD 510, the LD 520, the PDIC 570, and the FMD 580 are connected to a flexible printed circuit (FPC) 505 so that electrical connection can be achieved therebetween. A flexible printed circuit (which will be hereinafter abbreviated as FPC) is formed by providing a metal foil such as a copper foil in parallel with an insulating sheet on which a plurality of circuit conductors are printed, and further providing a protective layer thereon. The optical pickup device 501 includes various elements as described above. Here, while the optical pickup device 501 includes structural elements (not shown) other than those described above, these elements are omitted in FIG. 7 for the sake of convenience.
The optical pickup device 501 is used for reading or recording data such as information in media. Here, the media include various types of optical disks including, for example, read-only optical disks such as CD-ROMs and DVD-ROMs, recordable (write-once) optical disks such as CD-Rs and DVD±Rs, and writable/erasable or rewritable optical disks such as CD-RWs, DVD±RWs, and DVD-RAMs.
Here, “CD” is an abbreviation of a Compact Disk, and “DVD” is an abbreviation of a Digital Versatile Disk. Further, “ROM” in “CD-ROM” or “DVD-ROM” is an abbreviation of Read Only Memory, and therefore “CD-ROMs” or “DVD-ROMs” are read-only disks. Further, “R” in “CD-Rs” or “DVD±Rs” is an abbreviation of Recordable, and therefore “CD-Rs” or “DVD±Rs” are recordable disks. In addition, “RW” in “CD-RWs” or “DVD±RWs” is an abbreviation of Re-Writable, and therefore “CD-RWs” or “DVD±RWs” are rewritable disks. Also, “DVD-RAM” is an abbreviation of Digital Versatile Disk Random Access Memory, and is therefore readable, writable and erasable.
The optical pickup device 501 is used for reading data recorded on various optical disks or for recording data on various recordable or rewritable optical disks.
By supplying electric current to the LDD 510, the LD 520 emits a laser beam. At this time, the LD 520 generates heat, which causes a temperature change in the LD 520. The oscillation wavelength of laser in the LD 520 when the laser beam is emitted from the LD 520 depends on the temperature. Accordingly, as the temperature of the LD 520 changes significantly, the wavelength of the laser beam emitted from the LD 520 varies. Further, when electric current is supplied from LDD 510 to LD 520 to cause the LD 520 to emit a laser beam, the LDD 510 also generates heat. Thus, the LDD 510 and the LD 520 constitute a main heat source in the optical pickup device 501.
As one countermeasure against heat generated by the laser driver, a heat dissipation device in an optical head, in which a metal laser holder holding a semiconductor laser is coated with a heat dissipating coating having a heat dissipation effect, has been proposed.
In recent years, there has been a demand for further reduction in weight and size of an optical disk apparatus (not shown) or the optical pickup device 501 which is mounted in an optical disk apparatus. To meet such a demand, it is proposed to use a housing made of a resin, in place of a metal housing as conventionally used, for containing the LD 520, the diffraction grating 530, the intermediate lens 540, the half mirror 550, the objective lens 560, the PDIC 570 or the like, thereby achieving reduction in weight. When a metal housing is replaced by a housing made of a resin, the weight of the optical pickup device 501 can be reduced.
However, a housing made of metal is superior in heat conductivity to a housing made of resin. Therefore, when a resin housing is used in an optical pickup device, there is a problem that heat generated by the LD 520 is difficult to dissipate.
As already described above, the oscillation wavelength of laser when the laser beam is emitted from the LD 520 depends on the temperature. Accordingly, as the temperature of the LD 520 changes significantly, the wavelength of laser beam emitted from the LD 520 also changes. There is therefore a problem that when the LD 520 is heated by heat generated by the LD 520 itself, the wavelength of the laser beam emitted from the LD 520 varies and this prevents the LD 520 from emitting a laser beam at a fixed wavelength.
In order to facilitate heat dissipation of the LD (light emitting element) 520, it is proposed that a large number of heat dissipation fins (not shown) be provided on the LD (light emitting element) 520 or the fixing members of the LD (light emitting element) 520, for example. This proposed structure, however, causes another problem that provision of a large number of heat dissipation fins increases the size of the optical pickup device 501.
There is also a demand, from assembling manufacturers of an optical pickup device or assembling manufacturers of an optical disk apparatus, for optical pickup devices which can resist somewhat rough handling.